Making a wave texture orientate properly
You need to control the texture coordinates (and you need to add a gradient texture as well).

Let's break it down.

You are not using any coordinates to map the texture. By default Blender will use Generated coordinates to map procedural texutes. Generated coordinates will put the center of the texture in the lower left corner of the bounding box for the object.



Use object coordinates, they start at the origin of the object. 

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To learn more about texture coordinates watch Bartek Skorupa's video: Manipulate Texture Coordinates like a Boss